Photodynamic therapy (PDT) treats tumors by a combination of photosensitizer molecules that are preferentially taken up by the tumor cells and illumination with light. The light excites the photosensitizer molecules to become active radicals through the formation of negatively charged singlet oxygen that kills the tumor cells. PDT is a very attractive therapy since it leaves connective tissue intact, while destroying tumor cells.
With PDT it is difficult to control and measure the concentration of the photosensitizer drug in the tissue. The toxic reaction needs the drug, oxygen (tumors are often hypoxic) and light. For providing the drug, there are concepts of oral, intravenous and topical administration (injection into the tumor). A problem with PDT is that it is difficult to administer the required light dose in a proper fashion. Too little light will save connective tissue, but also leave tumor cells unaffected, while too much light will lead to damage of connective tissue.
For example PDT is of utmost importance for treatment of prostate cancer, as this disease remains indolent for long times but can exhibit lesions that turn aggressive and need to be destroyed—which calls for a repeatable therapy. In contrast, external beam (photon and Ion) therapy and brachytherapy leave irreversible permanent damage behind in all tissue, and render tissue boundaries invisible, which is a problem for surgeons in case subsequent surgical resection is planned. PDT can also advantageously be applied for treatment of cancer in the mouth, esophagus, lung, and cervix. It may also be used for treatment of breast cancer.
WO 2008/062000 A1 discloses a PDT treatment method, where measurements of treatment parameters are done prior to the treatment and updated after a treatment step. Thus, the method suffers from poor control of the light administering during treatment.